The present invention relates to a method for mounting a semiconductor element to a circuit board, which is used for electrically connecting projecting electrodes, i.e., bumps on the semiconductor element to electrodes on the circuit board, and a semiconductor device having the semiconductor element mounted on the circuit board according to the method.
U.S. Pat. No. 4,661,192 discloses in the published specification a method for forming bumps on a semiconductor element by ball bonding and a method for bonding the semiconductor element. The conventional methods will be described.
In FIG. 25, a high voltage of several thousand volts is impressed from a discharge electrode (torch) 17 to a leading end 16a of an Au wire 16 extending from a leading end of a capillary 15. While a discharge current flows between the torch 17 and the leading end 16a of the wire, the wire 16 is heated to a high temperature from the leading end 16a and then melted, resulting in a gold ball 18 as shown in FIG. 26. The ball 18 is fixed onto an electrode 3a of a semiconductor element 3 by the capillary 15, thereby forming a bump bottom part 19 as in FIG. 27. Thereafter, the capillary 15 is pulled upward as in FIG. 28. The capillary 15 is looped above the bump bottom part 19, so that the wire 16 is tightly adhered to the bump bottom part 19, and then the wire is cut. A bump 20 is formed in this manner.
A semiconductor element 3 having the bumps 20 formed as above is pressed against a stage 14 having a flat face as shown in FIG. 29. As a result thereof, leading end parts of the bumps 20 are flattened. Then, as indicated in FIG. 30, the semiconductor element 3 with the flattened bumps 20 is brought into contact with a conductive adhesive 6 applied on a stage 5 to transfer the conductive adhesive 6 to the flattened bumps 20. In FIG. 31, the semiconductor element 3 having the bumps 20 with the conductive adhesive 6 transferred thereon is registered with electrodes 2 on a circuit board 1 and then fixed thereto, whereby the semiconductor element is electrically connected to the circuit board 1.
As described hereinabove, conventionally, the semiconductor element 3 and circuit board 1 are bonded only by the conductive adhesive 6 transferred to the bumps 20 of the semiconductor element 3. As such, the bonding between the semiconductor element 3 and circuit board 1 has merely a bonding strength of an area at the leading ends of the bumps 20 of the semiconductor element 3, and the conductive adhesive 6 exerts a strength as low as 1-2.0 g at every bonded part because only a small amount of the conductive adhesive 6 is used so as to lower a volume resistivity. Such inconveniences are realized when the bonded part cracks because of a warp of the circuit board 1 or a stress when the conductive adhesive 6 is set, a connection resistance value is increased, and a disconnection at the bonded part arises.
An object of the present invention is therefore to provide a method for mounting a semiconductor element to a circuit board whereby connection reliability and connection strength are enhanced in bonding between the semiconductor element and circuit board, and a connection resistance value is stabilized to be low. Another object is to provide a semiconductor device having a semiconductor element mounted to a circuit board by the method.
In order to accomplish the above-described objects, according to a first aspect of the present invention, a method is provided for mounting a semiconductor element to a circuit board. The method comprises:
disposing an insulating adhesive having a property of shrinking upon being set, at least at either of opposite faces confronting each other of the circuit board and the semiconductor element;
registering the circuit board and the semiconductor element so that an electrode on the circuit board corresponds to a projecting electrode on the semiconductor element;
coupling the opposite faces of the circuit board and semiconductor element by the insulating adhesive; and
setting the insulating adhesive, so that the electrode on the circuit board and the projecting electrode on the semiconductor element are electrically connected through the shrinkage of the insulating adhesive such that the semiconductor element and circuit board are fixed in a coupled state.
A semiconductor device according to a second aspect of the present invention has a semiconductor element mounted to a circuit board according to the above mount method of the first aspect.
According to the mount method for a semiconductor element to a circuit board of the first aspect and the semiconductor device of the second aspect, the semiconductor element and circuit board are connected with the use of the insulating adhesive, and therefore connected rigidly in comparison with the conventional art whereby the connection is achieved only by the projecting electrodes of the semiconductor element and the electrodes of the circuit board. Therefore, a connection resistance value at a projecting electrode of the semiconductor element and a corresponding electrode of the circuit board is reduced and less varied, and at the same time, connection strength is high, thereby realizing highly reliable bonding.